The airline industry continues to undergo an evolution leading to longer range, lower cost, greater capacity aircraft as the demand for air travel continues to rise. With the evolution of higher efficiency, higher thrust engines, it is possible for the aircraft manufacturers to produce twin engine planes with ranges and payloads far exceeding expectations. As the range of these new advanced aircraft increases opening up routes never before available, the greater the likelihood that the aircraft will be a long way from a suitable airport in case of emergency. To minimize the risk to these aircraft and their passengers and cargo, the Federal Aviation Administration (FAA) and other world regulatory authorities have imposed strict safety requirements for the certification and operation of twin engine planes.
In the United States of America, the FAA has imposed a stringent set of requirements which must be met before certification of a twin engine aircraft is granted for extended twin engine operation (ETOPS). These increased requirements affect nearly every system on the aircraft and are designed to ensure that the plane can continue to fly safely to a suitable airport in case of an emergency, such as the loss of one of the two engines. One of the systems affected by these increased ETOPS requirements is the electric power generating system (EPGS).
A typical EPGS has one generator mounted on each main engine to produce the required electric power for the aircraft. The electrical output from each of these generators, assuming more than one engine, is coupled through a plurality of relays or contactors to the various loads and systems which require electric power. Some of the larger electric power generating systems operate in parallel to allow the total system load to be shared equally by all of the generators, and to allow greater fault clearing capability. Other systems operate to maintain complete isolation between the generators to ensure that no single fault can cause the loss of all electric power. Regardless of its normal operating mode, parallel or isolated, all systems are required by the FAA to achieve or maintain at least two channel electrical isolation during certain flight phases, such as landing for example. With a two engine aircraft, the available sources of primary electric power only number two to start with, and the loss of an engine will not allow two isolated channels. In order to be certified to the higher ETOPS requirements, a third source of electric power capable of operating with either engine inoperative was needed.
The solution to this problem, as illustrated in FIG. 1, was to include a small variable speed back-up generator 100, 102 on each engine in addition to the main integrated drive generators (IDGs) 104, 106 manufactured by the assignee of the instant invention. The output from each of these generators is coupled to a single back-up converter 108 which is available to supply certain loads during required periods of operation. Since the converter only requires power to be supplied from one of the two back-up generators (the primary generator), the other back-up generator (the standby generator) could be left de-energized to conserve power. However, since the operation of this standby generator must be verifiable and verified prior to and during each flight, a separate voltage regulator is required for this standby generator. This second voltage regulator is required to maintain output voltage regulation at a level below that of the primary generator to ensure that only the primary generator supplies the system loads. This requirement of a second voltage regulator increases the weight, cost, and complexity, and decreases the reliability of the system.
The instant invention is directed at overcoming this problem by providing a system to verify the operational readiness of the standby generator prior to and during flight to ensure maximum system safety while reducing system weight, cost, and complexity, and increasing system reliability.